Embodiments of the present invention generally relate to a system and method of deicing water within a receptacle, such as a pond, birdbath, or the like. More particularly, embodiments of the present invention relate to systems and methods for temperature sensing in a deicer.
Heating or deicing systems have commonly been used to maintain unfrozen areas in fluids such as water. For example, deicing systems may be used in water tanks for livestock, fish ponds, and the like. Early deicers burned wood, coal, or gas while most deicers today are electric. A typical deicing system includes a heater coil. The heat from the coil is transferred to the fluid to keep the fluid from freezing. Electric deicers typically range from 1000 to 1500 watts and may include thermostats that are commonly used to turn the unit on or off in order to introduce heat into the fluid when freezing conditions exist.
Many property owners have ponds located within their property. During winter months in colder climates, the ponds tend to freeze over with ice. When the ponds freeze over, toxic gases are trapped under the ice and pose a hazard to fish living within the pond. If the frozen surface is not broken in order to allow toxic gases to escape, the water below the frozen surface may become overly concentrated with nitrates, for example. Thus, the ice typically is broken in order to allow the toxic gases to escape.
In order to gain access to water below the surface for various activities and provide a path for toxic gases to escape, the frozen surface of the water is typically broken, drilled, or the like, in order to provide an accessible path to the water below. However, conventional methods of providing access to the water are typically labor-intensive, time-consuming, and typically do not prevent subsequent freezing.
As an alternative to conventional methods, pond heaters may maintain an ice-free area within a body of water. However, typical pond heaters are expensive to operate because they operate between approximately 1000 and 1500 watts or more, and, as such, may be dangerous.
Deicers typically are one of three types: (1) floating deicers, wherein the heating element is suspended from a floatation device such that it operates near the surface of the fluid; (2) sinking deicers, wherein the deicer rests upon the bottom of the pond or tank, usually attached to a guard such that the heating element is not in direct contact with the bottom; or (3) drain plug deicers mounted through the drain hole in a livestock tank.
Each of these three types has its own advantages and disadvantages. A floating deicer can more accurately measure the temperature at the surface where freezing will occur, thus it can be set more accurately to turn on at the optimum temperature. However, a deicer on the surface is also within reach of animals that may interfere with its operations or attempt to flip it out of the tank.
Sinking deicers, on the other hand, are often out of sight. However, because the deicer is positioned near the bottom of the fluid and freezing occurs at the top, a temperature gradient between the top and bottom of the fluid may exist. As such, the deicer may turn on at a higher temperature and heat more of the fluid, thereby having a reduced efficiency when compared to a floating deicer.
Drain plug deicers conveniently mount through the drain hole of a livestock tank where they are out of reach of animals and the cord can be protected. However, they also share the disadvantages of a sinking deicer, and have the additional disadvantage of requiring the tank to be drained in order to install the unit.
Deicers typically contain a thermostat to activate the heating element whenever the fluid temperature falls to a point where freezing may occur. The following discussion assumes the fluid is water, with a freezing point of 32 degrees Fahrenheit (F.). In deicers with thermostats, the thermostat will normally turn on at around 40 degrees F. and will turn off after the water temperature has risen a number of degrees. While the water will not freeze until it reaches 32 degrees F., the set point for turning on the thermostat is usually situated around 40 degrees F. to accommodate the uncertainty in accurately determining the set point during production. That is, the set points of a batch of thermostats designed to turn on at 40 degrees F. may actually have a spread of +/−7 degrees F. around that temperature.
Thermostatically-controlled deicers include a thermostat that is placed in series with the heating element. The deicers are normally preset to turn on when the fluid temperature reaches a value approaching the freezing point and turn off when the fluid temperature reaches a value tens of degrees above the freezing point. The thermostat may include bimetal arms that serve as the electrical switch for the deicer. Thus, no additional components are required.
The thermostats used in deicers are typically of the bimetal type. Typical turn-on/turn-off set points are around 45 degrees F. and 70 degrees F., respectively. However, the actual on/off temperatures of the thermostats are usually specified with a range of 5-8 degrees F. above and below these set points because, as mentioned above, the thermostat may have an actual spread of +/−7 degrees F. due to inaccuracy during production. While this range is necessary in order to keep the price of the thermostats down, it is not desirable from an operation standpoint since the deicer could turn on when the water temperature is only 50 degrees F. with no danger of freezing. For a 1500 watt deicer, the operation can therefore be needlessly expensive. Thus, it is highly desirable to have a deicer that is capable making more accurate temperature determinations and of making more intelligent decisions regarding temperature conditions.
The thermostat may also serve as a safety device when a thermal path is provided from the heating element to the thermostat such that it will shut off if excess heat is detected. Excess heating may occur if the heater is removed from the fluid, for example. A typical deicer contains a heating element rated at 1000-1500 watts. When submerged, the heating element of the deicer would normally run at a surface temperature of less than 150 degrees F. since the water rapidly transfers heat away from the heating element. Deicers with mechanical thermostats typically contain a thermal path from the heating element to the thermostat such that, in the absence of water, heat is transferred to the thermostat so that its temperature rises quickly and the thermostat is triggered to de-energize the heating element. The amount of time required to de-energize the heating element may be as much as a minute or more, during which time, the temperature of the heating element may rise to several hundred degrees. While the temperature may be too low to ignite paper, it can be high enough to cause burns to livestock or humans that come in contact with the heating element.
Another potentially harmful over-temperature condition may occur if the heating element is tilted such that only a portion of the heating element extends beyond the water while the thermostat is still submerged. In this case, the exposed portion of the heating element may overheat, but the thermostat will not register the over-heat condition because the thermal path from the exposed portion of the heating element to the thermostat is partially submerged and the water may dissipate the heat along that path. The heating element may glow red-hot and become hot enough to ignite paper or wood or melt the side of a plastic water tank. In addition, the exposed section of the heating element may cause severe burns to livestock or humans. Thus, a means for detecting over-temperature conditions, where all or a portion of the heating element is exposed, is desirable.
For any given thermostat, the response of the thermostat is dependent upon the set-point temperature, the rate of heat buildup in the thermostat, and the rate of heat loss from the thermostat.
Many thermostats have an adjustable set-point. A common example of this is a furnace thermostat in a home. The temperature at which the thermostat trips, or changes state, can be changed mechanically or electronically. Other thermostats, however, are non-adjustable and are preset to trip within a certain temperature range. These thermostats are typically set by mechanically adjusting the arms of a bimetal switch or the force upon those arms.
Regardless of the set-point of a thermostat, the thermostat's response is directly influenced by the rate at which heat is carried to and from the thermostat. For example, a hotplate may contain a thermostat to shut off power to the unit to prevent overheating, but if the hotplate is operated inside a freezer, the thermostat may never shut off because the heat may be carried away faster than it is produced.
Because thermal characteristics can vary greatly between different operating environments, and the desired response of deicers can vary between users, it is desirable to provide some means of controlling the response of a thermostat that would otherwise be non-adjustable.
Thus, it is highly desirable to have a deicer that is capable making more accurate temperature determinations and of making more intelligent decisions regarding temperature conditions. Further, a means for detecting over-temperature conditions, where all or a portion of the heating element is exposed, is desirable. In addition, it is desirable to provide some means of controlling the response of a thermostat that would otherwise be non-adjustable. Therefore, there exists a need for systems and methods for temperature sensing in a deicer.